1. Technical Field
This disclosure generally relates to replication of computer resources, and more specifically relates to data replication which combines synchronous and asynchronous methods to provide fast and efficient real time data replication.
2. Background Art
There is an ever increasing need for reliable high speed data processing systems. These data processing systems require data repositories that can provide critical data at any moment in time in the face of interruptions caused by hardware failure, software failure, natural disaster, etc. To achieve the necessary data availability, many data systems utilize remote data repositories to backup and store critical data. A common means of fast data backup to the remote data repositories is by database replication.
With database replication, the database management system can make informed decisions on whether to write data to multiple local storage devices or to a local storage device and a remote storage device, but such synchronization comes at a significant performance penalty. The technique of replicating data to multiple storage devices simultaneously is also known as mirroring. Data replication is typically either synchronous or asynchronous. In synchronous data replication, the replicated database is kept updated with current information in the primary database. In this manner, critical data can be accessible at all times. Ensuring transaction and record consistency often results in data transmission latency when a large number of data transmissions to remote sites are necessary with each database update. Consequently, application performance may be slowed to unacceptable levels.
Database replication systems also use asynchronous replication. In asynchronous systems, the data in the replicated database is updated in batches or at specified intervals. While asynchronous systems use less system resources, they do not guarantee there will be no data loss on the replicated database if a failure of the primary database occurs. Therefore, applications that require no loss of data at the replicated database often cannot employ asynchronous replication and thus rely on slower synchronous replication techniques.
While asynchronous systems are faster and use less system resources, they do not guarantee there will be no data loss on the replicated database. Synchronous replication systems can guarantee no loss of data but are slower and have a higher cost to system resources. Thus there is a tradeoff between using asynchronous and synchronous data replication.